This disclosure generally relates to systems and methods for choosing a flight path of an aircraft. In particular, this disclosure relates to systems and methods for selecting the flight path of an unmanned aerial vehicle (UAV) in the event of an in-flight contingency.
Small UAVs must have access to communications and navigation signals for some parts of their missions, including landing. Planning for a nominal mission typically includes consideration of where and when these signals are available and where and when they are blocked. Many known software packages support this sort of planning.
Sometimes communication or navigation signals are blocked unexpectedly (e.g., by jamming) or by known factors (e.g., terrain) that only become relevant when some other contingency forces the UAV to depart from the nominal mission path. Examples of these other contingencies include an engine failure or flying an improvised route to pursue a suspect.
To illustrate the foregoing, consider a scenario in which a UAV in a mountainous region may be in line-of-sight to the operator. It is orbiting a surveillance target and staying in the “good communication and navigation” zone defined by pre-mission planning. Then the operator sends the UAV in an unplanned direction to support search and rescue. This takes the UAV behind the mountains, cutting communications at the nominal altitude. In such a situation, it would be undesirable to lose the UAV or abandon the mission.
Larger UAVs and manned aircraft often have redundant systems for communication (e.g., SATCOM) and navigation (e.g., inertial navigation) that enable them to respond to jamming and other contingencies without losing communication and navigation. That is, they have many spectral degrees of freedom. On the other hand, small UAVs typically cannot tolerate the weight, power, and volume needed for such redundant systems; accordingly, small UAVs rely on a single radio and a global positioning system (GPS) receiver. To deal with communication/navigation aspects of in-flight contingencies, such UAVs have few or no spectral degrees of freedom; instead, they must rely on degrees of freedom enabled by flight control.
One solution is manual selection of a path in real-time by the vehicle operator in response to an in-flight contingency. When a contingency requires a forced landing, the vehicle operator looks around (via the UAV's camera or on a map) for potential landing sites, takes his or her best guess as to which sites the aircraft can safely reach in light of the need for communication, picks one of those sites, and attempts to pilot the UAV to that site. Likewise for other deviations from the flight plan: the operator picks a path that he or she guesses will be safe and have adequate communications while accomplishing the mission objective.
Another solution is preprogramming a desired behavior of the UAV. When the UAV loses communication or loses its connection to a GPS signal, it executes a path pre-programmed by its operator prior to flight.
A further solution, for a contingency that requires a forced landing, is to provide a computer program that examines stored information about terrain, weather, aircraft performance characteristics, and terrain features such as airports, roads, power lines, or forests; chooses potential landing sites that can be reached within the performance limits of the aircraft; and either flies the aircraft to one of those sites or displays information to guide a vehicle operator to one of the sites. For flight planning, including ad hoc re-planning, this known solution provides a path from which the UAV can always reach a safe landing site within the kinematic limits of the UAV. This known solution does not consider communication or GPS connectivity constraints.
There is a need for systems and methods capable of assisting a UAV to choose a flight path that maintains access to communication and navigation signals in contingency situations.